1. Field of the Invention
This invention relates to MEMS based RF components and a method of fabrication thereof, using CMOS technologies. The components are parallel-plate microstructures with vertical motion and include variable capacitors, filters, adaptive matching networks, reconfigurable amplifiers and switches. A process of manufacturing the CMOS-MEMS RF devices uses a dry reactive-ion etching process and a wet etching process.
2. Detailed Description of the Prior Art
It is known to have electronic systems in which all of the components are integrated into a single small-size wafer and packaged as a chip. It is known in active semi-conductor process technology to have all of the components integrated into a single chip. However, with radio frequency (RF) passive components, as the transmitter chip size becomes smaller and smaller, RF passives remain a bottleneck for system miniaturization.
The advances of microelectronics manufacturing technology have led to system-on-chip; a process by which all the components of an electronic system are integrated into a single small size wafer packaged as a chip. Compared to the active semiconductor process technology, there has been less attention to the miniaturization of radio frequency (RF) passive components and as the transmitter chip size becomes smaller and smaller, RF passives remain a bottleneck for system miniaturization. RF micro-electro-mechanical system (MEMS) components are good candidates to substitute the bulky off-chip RF passives in the existing RF integrated circuits (RFICs) due to their good RF performance and miniaturized dimensions. The fabrication of these MEMS devices in a commercially available complementary metal-oxide-semiconductor (CMOS) technology can further enhance the system performance with respect to integration and manufacturing cost.
MEMS variable capacitors can be used as tuning elements in several RF systems including tunable filters, voltage-controlled oscillators (VCOs) and impedance matching networks. It is known to use MEMS technology to design variable capacitors with superior performance (See U.S. Pat. No. 6,373,682 to Goodwin-Johanson et al.; U.S. Pat. No. 6,418,006 to Liu et al.; U.S. Pat. No. 6,355,534 to Cheng et al; M. Bakri-Kassem et. al., “Two movable-plate nitride-loaded MEMS variable capacitor”, IEEE Trans. Microw. Theory Tech., vol. 52, no. 3, pp. 831-837, March 2004; M. Bakri-Kassem et. al.; “A high-tuning-range MEMS variable capacitor using carrier beams”, Can. J. Elect. Comput. Eng., vol. 31, no. 2, pp. 89-95, Spring 2006; A. Oz et. al., “CMOS-compatible RF-MEMS tunable capacitors”, IEEE MTT-S Int. Microw. Symp. Dig., vol. 1, pp. A97-A100, June 2003). These capacitors are classified as either lateral-interdigital or parallel-plate capacitors. Lateral-interdigital MEMS capacitors demonstrate a better linear tuning characteristic than parallel-plate capacitors, whereas parallel-plate capacitors exhibit a higher quality factor and lower parasitic inductance.
It is known in the art to use CMOS-compatible processes to fabricate lateral-interdigital MEMS devices as disclosed in U.S. Pat. No. 6,458,615 to Fedder et. al.; U.S. Pat. No. 5,970,315 to Carley et. al.; U.S. Pat. No. 7,026,184 to Xie et al.; A. Oz et. al., “CMOS-compatible RF-MEMS tunable capacitors”, IEEE MTF-S Int. Microw. Symp. Dig., vol. 1, pp. A97-A100, June 2003, each of which is incorporated herein by reference. Parallel-plate variable capacitors are known and can be designed for higher capacitance values with a smaller area, but have not been fabricated using CMOS processes.